1. Field of the Invention
The present invention relates to a touch panel for operating various electronic devices.
2. Background Art
In recent years, electronic devices including mobile phones and car navigation systems have been increasingly multifunctional and diversified. More and more such electronic devices with increased functionality and diversity have come to use a touch panel for switching the various functions. Through the light-transmissive touch panel disposed on the front surface of a display element such as liquid crystal, the user can touch it with a finger or a touch screen pen while monitoring the display of the display element disposed behind the touch panel. Such a touch panel is required to have excellent visibility and to provide reliable operation.
One example of the conventional touch panels is described as follows with reference to FIGS. 5 to 8. FIG. 5 is an exploded plan view of the conventional touch panel. FIG. 6 is a plan view of the wiring board of the touch panel. FIG. 7 is an exploded perspective view of the wiring board. FIG. 8 is a sectional view of the wiring board when seen from the direction of the arrow of line 8-8. In FIG. 8, the size in the thickness direction is enlarged for easy understanding.
Touch panel 100 includes upper substrate 101 and lower substrate 102, which are light-transmissive. Upper substrate 101 has upper conductive layer 103 on its bottom surface, and lower substrate 102 has lower conductive layer 104 on its top surface. Upper and lower conductive layers 103 and 104 are light-transmissive and made of indium tin oxide or the like. Touch panel 100 is connected to wiring board 150 and hence to the electronic circuit (not shown) of an electronic device via wiring board 150.
Lower conductive layer 104 is provided with a plurality of dot spacers (not shown) of insulating resin arranged at predetermined intervals on its top surface. A pair of upper electrodes 115A and 115B, which are made of silver or the like, extends on the left and right ends of upper conductive layer 103. Upper electrode terminals 105A and 105B are disposed at and connected to the ends of upper electrodes 115A and 115B, respectively, on the bottom of upper substrate 101. In a word, at an end along side 140 at which upper substrate 101 is connected to wiring board 150, upper electrode terminals 105A and 105B are disposed at the ends of upper electrodes 115A and 115B. Lower electrodes 116A and 116B extend on the top and bottom ends of lower conductive layer 104 in the direction orthogonal to upper electrodes 115A and 115B. Lower electrode terminals 106A and 106B are disposed at and connected to the ends of lower electrodes 116A and 116B, respectively, on the bottom of lower substrate 102. In a word, at an end along side 143 at which lower substrate 102 is connected to wiring board 150, electrode terminals 106A and 106B are formed. Consequently, upper electrode terminals 105A, 105B disposed on the bottom of upper substrate 101 and lower electrode terminals 106A, 106B disposed on the bottom of lower substrate 102 are aligned alternately as shown in FIG. 5.
Frame-like spacer 107 is provided at the outer periphery of either the bottom surface of upper substrate 101 or the top surface of lower substrate 102. Spacer 107 is provided on one or both sides thereof with an adhesive layer (not shown) in order to bond upper substrate 101 and lower substrate 102 together at their outer peripheries. Thus, spacer 107 allows upper conductive layer 103 and lower conductive layer 104 to be confronted with a predetermined spacing therebetween.
Wiring board 150 includes film-like substrate portion 108 formed of connection part 108A of a large width and wiring part 108B of a small width. In short, substrate portion 108 is divided into connection part 108A and wiring part 108B by dotted line 134. Connection part 108A is on the side, where wiring board 150 is connected to touch panel 100, for dotted line 134, and wiring part 108B having end 138 is on the side, where wiring board 150 is connected to the electronic circuit. Substrate portion 108 has upper wiring patterns 109A and 109B on its top surface and lower wiring patterns 110A and 110B on its bottom surface. Upper wiring patterns 109A, 109B and lower wiring patterns 110A, 110B are made of copper, silver, or the like.
Wiring board 150 further includes through-hole electrodes 110C and 110D, filled with silver or the like, for leading lower wiring patterns 110A and 110B to the top surface of wiring part 108B at the end 138 side. Thus, lower wiring patterns 110A and 110B are on the top surface together with upper wiring patterns 109A and 109B at the end 138 side. Consequently, upper wiring patterns 109A and 109B are arranged alternately with lower wiring patterns 110A and 110B on substrate portion 108.
Wiring board 150 further includes film-like upper cover sheet 111 and lower cover sheet 112. As shown in FIGS. 6 and 7, upper cover sheet 111 is slightly shorter than substrate portion 108 at both ends 136 and 138 so as to cover the top surface of substrate portion 108 except for the end area on the end 136 side and the end area on the end 138 side. Lower cover sheet 112 is slightly shorter than substrate portion 108 at end 138 so as to cover the bottom surface of substrate portion 108 except for the end area on the end 138 side.
In FIG. 5, the end area on the end 136 side indicates area 142 of a predetermined width from end 136 to dotted line 130. The end area on the end 138 side indicates area 144 of a predetermined width from end 138 to dotted line 132.
To make it easy to understand the structure, FIG. 5 does not show the individual shapes of upper and lower cover sheets 111 and 112, but shows how it would look if upper cover sheet 111 was transparent and lower cover sheet 112 could be seen through it. Upper electrodes 115A, 115B and upper electrode terminals 105A, 105B are shown in solid lines. FIG. 6, in which wiring board 150 is seen from above, does not show the part of upper wiring patterns 109A, 109B that is under upper cover sheet 111, and the part of lower wiring patterns 110A, 110B that is under substrate portion 108.
Area 142 of substrate portion 108 is sandwiched between upper substrate 101 and lower substrate 102. Upper wiring patterns 109A and 109B are bonded to upper electrode terminals 105A and 105B, and lower wiring patterns 110A and 110B are bonded to lower electrode terminals 106A and 106B using, for example, an anisotropic conductive adhesive (not shown) containing a synthetic resin and conductive particles dispersed thereinto. Touch panel 100 is formed as mentioned above.
Touch panel 100 is fixed on the front surface of a display element such as liquid crystal using an adhesive or the like, and then installed in the electronic device. At this moment, wiring board 150 is bent in order to be connected to the electronic circuit. Furthermore, upper wiring patterns 109A, 109B and lower wiring patterns 110A, 110B are electrically connected at end 138 to the electronic circuit by a connection connector, soldering, or other means.
In the above-described structure, the user touches the top surface of upper substrate 101 with a finger, a touch screen pen, or the like while monitoring the display of the display element disposed behind touch panel 100. This touching causes upper substrate 101 to bend and hence upper conductive layer 103 at the touched portion to come into contact with lower conductive layer 104.
On the other hand, the electronic circuit including a controller and a data processor (both not shown), applies a voltage sequentially to upper electrodes 115A, 115B and lower electrodes 116A, 116B via upper wiring patterns 109A, 109B and lower wiring patterns 110A, 110B of substrate portion 108. Thus, the voltage is sequentially applied to the left and right ends of upper conductive layer 103 and to the top and bottom ends of lower conductive layer 104 which are orthogonal to the left and right ends of upper conductive layer 103. When upper substrate 101 is pressed and then upper conductive layer 103 at the pressed portion comes into contact with lower conductive layer 104, a voltage change at the pressed portion is detected. Then, the electronic circuit including the controller and the data processor detects the pressed portion based on the voltage ratio of voltages changed before and after pressing. In this manner, touch panel 100 and the electronic circuit can switch between the various functions of the electronic device.
Wiring board 150 is formed as follows. Upper wiring patterns 109A and 109B are formed on the top surface of substrate portion 108, and lower wiring patterns 110A and 110B are formed on the bottom surface of substrate portion 108. Substrate portion 108 has a thickness of 20 to 30 μm, and upper wiring patterns 109A, 109B and lower wiring patterns 110A, 110B have a thickness of 10 to 15 μm. Then, upper cover sheet 111 and lower cover sheet 112 are applied to cover the top surface and bottom surface, respectively, of substrate portion 108.
Upper wiring pattern 109A, lower wiring pattern 110A, upper wiring pattern 109B, and lower wiring pattern 110B are arranged in this order at larger intervals at the end area on the end 136 side than at the end area on the end 138 side which is connected to the connector and the like. This means that these wiring patterns are larger in width in connection part 108A than in wiring part 108B. The reason for this is to ensure the connection between the wiring patterns and upper electrode terminals 105A, 105B, lower electrode terminals 106A, 106B using the anisotropic conductive adhesive or the like at end 136.
As described hereinbefore, substrate portion 108 has upper cover sheet 111 covering most of its top surface and lower cover sheet 112 covering most of its bottom surface. This causes connection part 108A to have large thickness and width, thereby making it hard to bend connection part 108A when substrate portion 108 is installed in the electronic device. In addition, after the installment, the elastic returning force of connection part 108A causes stress on the connection part between the wiring patterns and upper electrode terminals 105A, 105B, lower electrode terminals 106A, 106B at the top end of wiring board 150.